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The ages of globular clusters in NGC 4365 revisited with deep HST observations

The ages of globular clusters in NGC 4365 revisited with deep HST observations
The ages of globular clusters in NGC 4365 revisited with deep HST observations
We present new Hubble Space Telescope (HST) NIC3, near-infrared H-band photometry of globular clusters (GCs) around NGC 4365 and NGC 1399 in combination with archival HST WFPC2 and ACS optical data. We find that NGC 4365 has a number of globular clusters with bluer optical colors than expected for their red optical-to-near-infrared colors and an old age. The only known way to explain these colors is with a significant population of intermediate-age (2-8 Gyr) clusters in this elliptical galaxy. On the other hand, our result for NGC 1399 is in agreement with previous spectroscopic work that suggests that its clusters have a large metallicity spread and are nearly all old. In the literature, there are various results from spectroscopic studies of modest samples of NGC 4365 globular clusters. The spectroscopic data allow for either the presence or absence of a significant population of intermediate-age clusters, given the index uncertainties indicated by comparing objects in common between these studies and the few spectroscopic candidates with optical-to-near-IR colors indicative of intermediate ages. Our new near-IR data of the NGC 4365 GC system with a much higher signal-to-noise ratio agree well with earlier published photometry, and both give strong evidence of a significant intermediate-age component. The agreement between the photometric and spectroscopic results for NGC 1399 and other systems lends further confidence to this conclusion and to the effectiveness of the near-IR technique.
2041-8205
41-44
Kundu, Arunav
ece8dcd2-e6dc-4f02-a90b-016ba9b573ed
Zepf, Stephen E.
108fcc75-6611-48a3-b405-99737b38af85
Hempel, Maren
b5883fa0-caef-4379-89fe-bae499640814
Morton, David
db58a32a-6f7a-400f-8370-d847aa4d3f53
Ashman, Keith M.
c084aa86-ffbe-4e3a-815c-7620a46af1ab
Maccarone, Thomas J.
27e6101c-8fa4-41db-ba75-d2ee3d1a0c53
Kissler-Patig, Markus
15013729-5b95-48cd-90d1-aba98bff36f0
Puzia, Thomas H.
b625d688-ed67-462d-9691-6e7f9b69807b
Vesperini, Enrico
18776122-d88f-4648-9338-ae8b48f0cfb0
Kundu, Arunav
ece8dcd2-e6dc-4f02-a90b-016ba9b573ed
Zepf, Stephen E.
108fcc75-6611-48a3-b405-99737b38af85
Hempel, Maren
b5883fa0-caef-4379-89fe-bae499640814
Morton, David
db58a32a-6f7a-400f-8370-d847aa4d3f53
Ashman, Keith M.
c084aa86-ffbe-4e3a-815c-7620a46af1ab
Maccarone, Thomas J.
27e6101c-8fa4-41db-ba75-d2ee3d1a0c53
Kissler-Patig, Markus
15013729-5b95-48cd-90d1-aba98bff36f0
Puzia, Thomas H.
b625d688-ed67-462d-9691-6e7f9b69807b
Vesperini, Enrico
18776122-d88f-4648-9338-ae8b48f0cfb0

Kundu, Arunav, Zepf, Stephen E., Hempel, Maren, Morton, David, Ashman, Keith M., Maccarone, Thomas J., Kissler-Patig, Markus, Puzia, Thomas H. and Vesperini, Enrico (2005) The ages of globular clusters in NGC 4365 revisited with deep HST observations. The Astrophysical Journal Letters, 634 (1), 41-44. (doi:10.1086/498746).

Record type: Article

Abstract

We present new Hubble Space Telescope (HST) NIC3, near-infrared H-band photometry of globular clusters (GCs) around NGC 4365 and NGC 1399 in combination with archival HST WFPC2 and ACS optical data. We find that NGC 4365 has a number of globular clusters with bluer optical colors than expected for their red optical-to-near-infrared colors and an old age. The only known way to explain these colors is with a significant population of intermediate-age (2-8 Gyr) clusters in this elliptical galaxy. On the other hand, our result for NGC 1399 is in agreement with previous spectroscopic work that suggests that its clusters have a large metallicity spread and are nearly all old. In the literature, there are various results from spectroscopic studies of modest samples of NGC 4365 globular clusters. The spectroscopic data allow for either the presence or absence of a significant population of intermediate-age clusters, given the index uncertainties indicated by comparing objects in common between these studies and the few spectroscopic candidates with optical-to-near-IR colors indicative of intermediate ages. Our new near-IR data of the NGC 4365 GC system with a much higher signal-to-noise ratio agree well with earlier published photometry, and both give strong evidence of a significant intermediate-age component. The agreement between the photometric and spectroscopic results for NGC 1399 and other systems lends further confidence to this conclusion and to the effectiveness of the near-IR technique.

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Published date: November 2005

Identifiers

Local EPrints ID: 79515
URI: http://eprints.soton.ac.uk/id/eprint/79515
ISSN: 2041-8205
PURE UUID: 49218045-7cf4-4718-bfd8-0085083b7473

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Date deposited: 16 Mar 2010
Last modified: 14 Mar 2024 00:30

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Contributors

Author: Arunav Kundu
Author: Stephen E. Zepf
Author: Maren Hempel
Author: David Morton
Author: Keith M. Ashman
Author: Thomas J. Maccarone
Author: Markus Kissler-Patig
Author: Thomas H. Puzia
Author: Enrico Vesperini

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